Calendar/resource booking across email domains


The scenario that we have within my current organisation is that we have three related companies sharing a single office space. Two of the companies are using separate MS Exchange 2007 on premise environments, the third is using Microsoft Online.

We are looking for a solution whereby anyone from each of the three companies can 'book' meeting rooms from within Outlook/on their smartphones, and for all parties to have free/busy information.

There are many limitations handed down from HQ which affect our ability to form Active Directory domain trusts etc, so we have been tasked to find a way to achieve the intended objective without that.

All advice appreciated.

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cross forest free busy is the way forward or it you want more detail then full on GAL sync

The meeting rooms with the resource assistant running will make life easier to they will at least get an accepted or declined but to get the free busy you need the additional setup

i have this setup 3 way between 2007 and 2 just about works but it wasn't painless to setup

here is the technet link

here is a useful page from which has some slightly more useful details

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V1010Author Commented:
Many thanks for that - will explore those options.
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